Electronics > Beginners

Transformer primary multiple winding

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sdancer75:
Why this transformer has two separate windings on the primary side?

As far as I know, if they used for 110V or 220V selection, they should have to be connected about in the middle of the same winding, but these are totally separate between each other (infinite resistance). The resistance between connected pairs is about 0.8 Ohms for both of them.

Regards,

jmelson:
Most likely, you connect the outer two pins to your mains, either 120 or 240 V.  For 240, you connect the two inner pins together.  For 120 V, you connect each inner pin to the outermost pin near it.  It is done this way to make the bridging jumpers simplest on a PC board or terminal block.

Jon

T3sl4co1l:
That looks more like a ferrite core transformer from an SMPS, in which case the two windings are either the primary, and a "reset" or auxiliary winding.

Measure the turns ratio using a function generator set at 100kHz+.

Tim

FreddieChopin:

--- Quote from: T3sl4co1l on September 10, 2019, 07:54:40 pm ---That looks more like a ferrite core transformer from an SMPS, in which case the two windings are either the primary, and a "reset" or auxiliary winding.

Measure the turns ratio using a function generator set at 100kHz+.

Tim

--- End quote ---

Judging by the large and thick isulated prong on table I'd say it's more likely a HV trafo from old kinescope TV.

MagicSmoker:

--- Quote from: T3sl4co1l on September 10, 2019, 07:54:40 pm ---That looks more like a ferrite core transformer from an SMPS, in which case the two windings are either the primary, and a "reset" or auxiliary winding.

Measure the turns ratio using a function generator set at 100kHz+.

Tim

--- End quote ---

Yep, and if you look real closely at the wire terminations you can see that one pair uses a much thinner gauge of wire than the other, so almost certainly a reset winding for a forward transformer. Assuming the turns ratio is 1:1, that is*.



* - it's technically possible to use a non-unity turns ratio, to, for example, extend the duty cycle range at the expense of subjecting the switch to a higher reset voltage, but I've never seen this done commercially.

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